[petsc-users] Check vector for zeros

[Matthew Knepley]

On Thu, Jan 3, 2019 at 11:16 AM Stefano Zampini <stefano.zampini at gmail.com>
wrote:

> It already checks for zeros. See VecPointwiseDivide_Seq in
> src/vec/vec/impls/seq/bvec2.c
>

Yes, I was assuming he wanted to know if there were zeros and take some
other action.

  Thanks,

    Matt

> On Jan 3, 2019, at 5:12 PM, Matthew Knepley via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
>
> On Thu, Jan 3, 2019 at 11:01 AM Florian Lindner via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
>
>> Hello,
>>
>> Happy New Year Everybody!
>>
>> I get a vector from a linear solve and is used a divisor in
>> VecPointwiseDivide. Clearly, I must check for zero entries before doing the
>> division.
>>
>> What is the best way to do so, especially performance wise?
>>
>> The only way I come up with so far, is to VecCopy, VecAbs and then check
>> for VecMin > eps. The VecCopy kind of scares me for the performance draw
>> back. I haven't found something like a VecAbsMin.
>>
>> Any better ideas?
>>
>
> I would write VecAbsMin() yourself,
>
>
> https://bitbucket.org/petsc/petsc/src/bd27d3f284687498e4c4678d234c0e308a5bc236/src/vec/vec/utils/vinv.c#lines-299
>
> https://bitbucket.org/petsc/petsc/src/bd27d3f284687498e4c4678d234c0e308a5bc236/src/vec/vec/utils/vinv.c#lines-1510
>
> It should only be about 8 lines.
>
>   Thanks,
>
>     Matt
>
>
>> Thanks,
>> Florian
>>
>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>
>
>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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